1. Technical Field
The present invention relates to an image forming apparatus.
2. Description of Related Arts
An image forming apparatus using the electrophotographic method forms an image based on image information by exposing an image carrier such as a photoreceptor drum to laser light Alight irradiation device is provided with a laser diode or the like serving as a light source of the laser light, as well as a collimator lens, a fθ lens, and so forth. A light irradiation device irradiates laser light onto a photoreceptor drum through such components. A Light irradiation device forms a latent image corresponding to image information on a photoreceptor drum by exposing photoreceptor drum, which includes photosensitive materials on its surface, to the laser light.
A distance from a photoreceptor drum to a light irradiation device is adjusted so that a focal position of the laser light does not move, and then the light irradiation device is fixed to a partition wall or the like in an image forming apparatus. However, structural components of a light irradiation device are subject to volume change such as thermal expansion, due to heat from laser light and temperature fluctuation in an environment, whereby a focal point of the laser light for exposure of the photoreceptor drum may be shifted in location. Therefore, a problem arises due to difficulty in accurately focusing on a photoreceptor drum to form an image, and hence forming an image with superior quality.
A technique using a supporting member which supports a fθ lens is proposed for the purpose of correcting a shifted focal point due to temperature rise of the fθ lens (See Japanese Patent Application Publication No, H09-159954, for example). According to this technique, a supporting member is also thermally-expanded so that it can correct a shifted focal point due to temperature rise of a fθ lens. The expanded supporting member can adjust to thermal expansion of the fθ lens, thereby preventing degradation of image precision.
According to the technique disclosed in Japanese Patent Application Publication No. H09-159954, position variation of an imaging surface due to temperature rise of a fθ lens may be corrected, but temperature fluctuation of other components of a light irradiation device is not taken into consideration whatsoever. In other words, this technique can only achieve correction of a shifted focal point of laser light due to temperature fluctuation of a fθ lens. Considering that a shifted focal point of laser light can be caused by temperature fluctuation of a fθ lens as well as various other components, this technique can hardly correct a shifted focal point of laser light which results from combined position variation in a light irradiation apparatus as a whole.
The present invention is intended to address the above-described problems and to provide an image forming apparatus which is capable of correcting a shifted focal point of laser light generated by a light irradiation device as a whole, due to volume change of each component associated with temperature fluctuation.